This invention relates generally to nondestructive evaluation of metallic structures and more particularly to methods and apparatus for inspecting electrically conductive material.
Surface cracks and subsurface flaws in metallic structures can produce catastrophic failures in critical components or structural elements. Eddy current probes can be used to determine the severity of such cracks and flaws in the case of metallic components and structural elements. Configurations of pulsed eddy current two-dimensional array probes are known that utilize a two-dimensional sensor array probe system with a data visualization component for electrically conducting component inspection. The probe uses a two-dimensional array of magnetic field sensors for inspection of electrically conducting components without requiring mechanical scanning.
Metallic objects can also suffer corrosion loss. For example, a wall of a steel container, a pipe, or a plate may be locally affected by corrosion. In some cases, visual inspection of the corroded region may be impractical because of lack of access to the corroded region. Inspection of such objects may require a through-transmission technique that can detect corrosion on one side of the object with a sensor located on the opposite side. Pulsed eddy current is known to be capable of this type of measurement in conducting materials. However, the pulsed eddy current can be difficult to interpret quantitatively because the relationship between the response and the material properties of some objects is complex. For example, a pipeline or vessel wall may be so dirty as to preclude a visual inspection of the object. Moreover, a significant and spatially varying stand-off may be presented between the pulsed eddy current sensor and the actual surface of the object. This stand-off further complicates interpretation of eddy current responses.